1. Field of the Invention
This invention relates to improvements to a vaccum processing chamber used in semiconductor manufacturing. More particularly, it relates to an improved slit valve door for sealing apertures formed in the walls of such a chamber.
2. Background
During the manufacture of semiconductors, it is necessary to deposit or etch layers of various materials on a semiconductor wafer. This is typically done in a deposition or etch chamber of a processing apparatus, the operation of which is illustrated with reference to FIG. 1 of the accompanying drawings.
In a typical processing apparatus, a number of silicon wafers 10 are stacked in a wafer elevator 12. Individual wafers 14 are sequentially removed from the elevator by means of a robot arm 16 and inserted into a particular chamber 18 through an open aperture or slit 19, which is typically rectangular and barely accommodates the blade of the robot carrying the wafer 14.
In this figure, four independent chambers 18, 18.1, 18.2, and 18.3 are shown. Each chamber has its own slit, 19, 19.1, 19.2, and 19.3, respectively, and the robot arm 16 services all four chambers. Once the wafer 14 has been inserted into the chamber, the aperture 19 is closed by a mechanism generally referred to as a slit valve closure mechanism 20. For the sake of clarity, only one closure mechanism is illustrated. In practice, however, each slit 19, 19.1, 19.2, and 19.3 has its own closure mechanism. After the slit 19 is closed, the fabrication process commences, which typically involves pumping the chamber to a reduced pressure, or injecting a reactive processing gas into the chamber, or a combination thereof. Thus, the chamber must be environmentally isolated and the slits must be vacuum sealable. Once the process has been completed, the closure mechanism 20 is operated to open the slit 19. The wafer 14 is then removed from the chamber 18 by the robot arm 16 and inserted into another processing chamber 18.1 or returned to the rack 12.
FIG. 2 illustrates one possible mechanism for opening and closing the slit valve door 21. Other mechanisms do, however, exist. Two examples are described in U.S. Pat. No. 5,275,303, the disclosures of which are incorporated herein by reference. The closure mechanisms 20 shown in FIGS. 2 and 2A includes a slit valve door 21, which comprises an aperture cover plate 22 and a seal 30. The closure means, as illustrated, in FIG. 2 appears to have only one linkage 28. This is as a result of the particular view depicted and it is usual for the closure means to include at least two identical and parallel linkages respectively positioned at the opposite ends of the slit valve door 21. However, the linkage 28 in FIG. 2A may be a pneumatically actuated rod.
In FIG. 2, the slit valve door 21 is shown to close and seal an aperture 19 in the sidewall 24 of the semiconductor reaction chamber 18. The linkage 28, in cooperation with unillustrated pivots, moves the door 21 from an open position 21' (shown in broken lines) 21' away from the chamber sidewall 24 to the sealing position shown by the position of the door 21. To enhance the seal between the door 21 and the wall 24 of the chamber, a circumferential O-ring 30 is fitted into a groove 40 in the face 26 of the door 21. Typically, this O-ring is made of a resilient, compressible, and heat-resistant material. Most commercial O-rings are composed of an elastomeric material.
As illustrated in FIG. 3, the O-ring 30 is typically retained in a dovetail groove 40 formed in the wall-facing face 26 of the door 21. The O-ring 30 is press-fitted into the groove 40. As can be seen from the illustration, the side surfaces 42 of the groove 40 slope inwardly up toward the face 26 to form a restriction 46 at the face 26. This restriction is narrower than the diameter of the O-ring 30. Once the O-ring 30 has been pressed past the restriction 46, it is retained between the restriction 46 and the bottom surface 44 of the groove 40.
It is well known in the semiconductor manufacturing industry that during processing, contamination of the interior atmosphere of the chamber must be kept to a minimum, as such contamination is detrimental to deposition and related procedures, as well as to the integrity of the semiconductor wafer produced. The O-ring seal is intended to prevent the leakage of process gases through the slit 19 out of the process chamber and to prevent atmosphere from entering, thus reducing contamination therefrom.
Unfortunately, the prior art device described above does not seal the slit 19 as well as might be desired. Because the restriction 46 is narrower than the O-ring 30, the O-ring 30 must be forced past the restriction 46. This can damage the sealing surfaces of the O-ring 30, resulting in leakage of gases into or out of the reaction chamber. The O-ring 30 may also twist during insertion or be unevenly tensioned after insertion. In either case, the O-ring 30 does not have a uniform dimension and does not seat properly in the dovetail groove 40. This results in poor performance and short life, as well as a less effective seal.
Another problem is illustrated in FIGS. 4 and 4a, which is a plan view onto the relevant portion of the face 26 of a prior art slit valve door with a dovetail groove 40. This groove 40 is typically machined into the door by a router with a dovetail bit. The dovetail groove 40 is narrower at its opening 41 than at its bottom surface 44, as indicated in FIG. 3. This makes the groove 40 difficult to machine in such a way that it is uniform along its entire length and such that it does not begin or terminate at an edge of the face 26. Although a uniformly dovetailed groove could be achieved by starting the groove 40 at an edge of the face 26, this is generally considered less ideal than starting the groove 40 by simply plunging the router bit into the face 26. The router bit then travels in a closed loop, cutting the dovetail groove 40, and terminates at its starting point. This procedure results in a hole 48 at the starting point that is wider than the opening 41 of the groove and whose width is that of the bottom surface 44 of the groove (shown in FIG. 3). In tile region of the hole 48, the restriction 46 of FIG. 3 does not exist and thus there is no retention of the O-ring 30 at that point. This adversely affects the sealing ability of the O-ring 30.
In order to facilitate the removal of the O-ring 30 from the dovetail groove 40 which retains it, a small groove 50 is cut in the face 26 such that it is orthogonal to the groove 40 and such that it has a lower surface even with the groove's bottom surface 44. This allows the O-ring 30 to be pried out by means of a small tool inserted in the small groove 50 below the O-ring 30. This creates two problems. First, the O-ring 30 is no longer supported by the sides 42 of the dovetail groove 40. Second, use of the small tool to remove the O-ring 30 may result in damage to the bottom 40 of the dovetail groove near the intersection with the small groove 50. Both of these difficulties reduce the effectiveness of the O-ring seal 30.
Therefore, the need has arisen for a means of sealing an aperture in the wall of a deposition chamber or the like which can provide a more effective seal and further reduce contamination of the interior of the process chamber, which has a longer life in order to reduce downtime for replacing the seal, and which would preferably be easily retrofitted to existing valve closure mechanisms with a minimum amount of labor.